1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing stimulable phosphor sheets to a radiation passing through an object to have a radiation image of the object stored thereon, exposing the stimulable phosphor sheets to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to such an apparatus in which the stimulable phosphor sheets are circulated and reused for recording images and more particularly to such an apparatus in which the circulated and reused stimulable phosphor sheets can be conveyed by sectors and subjected to sectored image recording in the radiation image recording section.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed for example in Japanese Unexamined Patent Publication No. 56(1981)-11395 and U.S. Pat. Nos. 4,258,264, 4,315,318, 4,387,428 and 4,276,473, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, with regard to a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load such a mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects on the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets to a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examinations. This is very advantageous in practical use.
From the aforesaid viewpoint, the applicant proposed in U.S. patent application Ser. No. 037,119, which is a continuation of U.S. patent application Ser. No. 600,689 a radiation image recording and read-out apparatus comprising:
(i) a circulating and conveying means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(ii) an image recording section positioned on said circulation path for recording a radiation transmission image of an object on said stimulable phosphor sheet by exposing said stimulable phosphor sheet to a radiation passing through said object,
(iii) an image read-out section positioned on said circulation path an provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored thereon in said image recording section, and a photoelectric read-out means for detecting light emitted from said stimulable phosphor sheet scanned with said stimulating rays to obtain an electric image signal, and
(iv) an erasing section for, prior to the next image recording on said stimulable phosphor sheet for which the image read-out has been conducted in said image read-out section, releasing the radiation energy remaining on said stimulable phosphor sheet,
whereby said stimulable phosphor sheet is circulated through said image recording section, said image read-out section and said erasing section and reused for radiation image recording. The erasing section in this apparatus can be arranged to carry out an erasing method as disclosed, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,470,619.
The radiation image recording and read-out apparatus of this construction meets the various aforesaid needs while also making it possible to carry out the radiation image recording and the reprocessing of the used stimulable phosphor sheets with very high efficiency.
In radiography, however, there are occasions when it is desirable to be able to view and compare two images of the same object recorded under different conditions or by different methods. For example, it is frequently desirable to be able to compare front and side images of the same human body or to compare images of the same object recorded before and after the injection of a contrast medium. At such times it is convenient if the two images can be recorded on opposite halves of one and the same stimulable phosphor sheet.
With the aforesaid radiation image recording and read-out apparatus it is possible to first record the two images to be compared on separate stimulable phosphor sheets and then to reproduce these images on a single photographic film, thus obtaining the same effect as when the two images are recorded on the same stimulable phosphor sheet. However from the point of reducing running costs by reducing the number of stimulable phosphor sheets required, and of shortening the processing time, it is preferable to be able to record the two images on opposite halves of the same stimulable phosphor sheet.
The advantage of reduced running costs obtainable by recording plural images on the same sheet can of course be enjoyed not only when image pairs are recorded for comparison but in any case where two or more images are recorded on a single sheet.
For recording two or even three or more images on different sectors of a single stimulable phosphor sheet (hereinafter referred to as sectored image recording) it is conceivable to use a method wherein the radiation field diaphragm is moved, a method wherein the radiation source is moved, or a method in which the sheet is moved and the size of the radiation field is reduced during sectored image recording without moving the radiation field diaphragm. Among these methods, the last mentioned is the best since it is the simplest to apply practically and does not require complex modifications in the structure of the radiation image recording and read-out apparatus.